1. Field of the Invention
This invention relates to a data recording apparatus, and more particularly, is suitably applicable to a data recorder for recording digital record data on a magnetic tape with a helical scanning system using a rotational drum.
2. Description of the Related Art
As a data recorder, there is that which the ID-1 format, which has been standardized by America National Standards Institute (ANSI), is applied to.
In this ID-1 format, only recording format for record data and footprint, such as track length, track width and track angle of a magnetic tape and recording wavelength, has been prescribed, but rotational rate of a rotational drum (speed of a recording head), running speed of a magnetic tape, the number of recording heads, and others are not especially prescribed.
Therefore, in this kind of data recorder, it is able to perform variable-speed controlling of multiplying relative speed of the recording head relative to the recording track direction of the magnetic tape by 1/1, 1/2, 1/4, 1/8, 1/16, 1/24, etc., so that it is able to record/reproduce the record data with a desired transfer rate between about 100 Mbps/channel to about 4.2 Mbps/channel, for instance.
Therefore, this kind of data recorder is broadly utilized for such uses that observation data is recorded and reproduced, keeping the pace with the transfer rate of analyzing apparatuses; as an example, observation data that is obtained from an artificial satellite and that is having relatively fast transfer rate is recorded in real time and, on the other hand, the recorded observation data is reproduced at a slower transfer rate than that of recording, and, as an another example, observation data that is obtained from astronomic observation, monitoring of road status (occurrence of a traffic accident, a traffic backup and others), etc., and that is having relatively slow transfer rate is recorded at the original transfer rate and, on the other hand, the recorded observation data is reproduced at a faster transfer rate than that of recording.
By the way, in this kind of data recorder, it is able to cause the rotational head to rotate at a relatively high speed and to secure a relative velocity between the recording head and the magnetic tape, so as to utilize the recording capability of short wavelength of the magnetic tape to its maximum, so that high density recording and high transfer rate can be realized, and, in this way, it is able to enhance the recording rate for 1 channel to about 100 Mbps as stated above.
However, in the case where the record data has been recorded at about 100 Mbps in this manner, the permeability of the recording head (if the frequency becomes high because of high transfer rate, the permeability lowers) and the frequency characteristics of the recording amplifier and others equipped within the data recorder would reach to their limits.
In this kind of data recorder, it is able to lower the recording rate to, for instance, 4.2 Mbps or so by rotating the rotational head at a relatively low speed, and the permeability of the recording head and the frequency characteristics of the recording amplifier and others of this case become ideal status, within the region having sufficient margin.
In this kind of data recorder, there was such a problem that if the transfer rate is relatively high, under the influences of the permeability of the recording head and the frequency characteristics of the recording amplifier and others, the edge portion of the waveform pattern of the recording current corresponding to the record data dulls, that is, a lowering phenomenon of the high-frequency component occurs, and rising of the amplitude occurs in the vicinity of the maximum frequency of the recording current due to the resonance in the circuit of the output side of recording amplifier including the recording head, so that the frequency characteristic of this recording current changes. As a result of this, if the transfer rate differs, then the quantities of delaying of the phase of short wavelength relative to the phase of long wavelength in the magnetization pattern that has been recorded on the magnetic tape on the basis of the recording current. That is, if the quantity of so-called peak shift differ and the transfer rate differs, the magnetization patterns do not coincide.
By the way, as a data recorder that solves such a problem, heretofore, there is that which is constituted using a linear first recording amplifier (which has been disclosed by this applicant in Japanese Patent Laid Open No.07800/92) for equalizing high-frequency-component highlighting operations that is comprised of plural filters to which frequency characteristics have been set, according to transfer rate, and a linear second recording amplifier (which has been disclosed by this applicant in Japanese Patent Laid Open No.067359/92) for equalizing band limitations that is comprised of plural filters to which frequency characteristics have been set, according to transfer rate.
In this case, this data recorder passes a record signal through a filter of the first recording amplifier corresponding to its transfer rate and hereby previously highlight the high-frequency component of the edge portion so as to equalize the high-frequency-component highlighting operation in the case where the transfer rate differs, and also passes the record signal through a filter of the second recording amplifier corresponding to its transfer rate and hereby restrain the amplitude of the high-frequency component from rising in the band of the vicinity of the maximum frequency so as to limit it and equalize limitation of the band in the case where the transfer rate differs.
However, since such a data recorder employs class A amplifiers whose efficiencies are about 50% as the first and the second recording amplifiers, the consumed power becomes relatively large, and radiation plates for radiating heat generated in the class A amplifiers are needed, and so the configuration of the whole data recorder is complicated and enlarged--that has been the problem.
So, as a data recorder for solving the problem that arises from employing such linear first and second recording amplifiers and for varying frequency characteristics of the recording current in accordance with the transfer rate, there is that which is constituted as shown in FIG. 1 (which has been disclosed by this applicant in Japanese Patent Laid open No.287804/95).
That is, in this data recorder 1 shown in FIG. 1, digital data D1 that is supplied from the exterior at the stated transfer rate and input clock signal CK1 corresponding to the digital data D1 are inputted to a signal processing circuit 2.
This signal processing circuit 2 exposes the record data D1 to the stated recording signal processing to produce record data D2 shown in FIG. 2A and then sends this data to an edge extracting circuit 4 of a recording amplifier 3 that is comprised of a switching amplifier, and besides converts the input clock signal CK1 into the first clock signal CK2 having the stated period T shown in FIG. 2B and then sends this to the edge extracting circuit 4.
The edge extracting circuit 4, which operates on the basis of this first clock signal CK2, detects the time at which the record data D2 rises to the logical level [1] and also the time at which it falls to the logical level [0], and then, on the basis of this detection result, generates a timing signal ES that is showing the position to highlight its high-frequency component previously, in expectation of lowering of the high-frequency component of the edge portion. Then, the edge extracting circuit 4 sends the record data D2 to the first switching unit 5, and sends the timing signal ES to the second switching unit 6.
In this connection, the timing signal ES is synchronized with the first clock signal CK2, and raises to the logical level [1] during only the period T of the first clock signal CK2 from the time at which the record data D2 rises to the logical level [1] and also the time at which it falls to the logical level [0], respectively, as shown in FIG. 2C, so that the high-frequency component highlighting positions are shown by the logical level [1].
The first contact a.sub.1 of the first switching unit 5 is connected to one of two coils, which are coupled with an intermediate tap 7A, that have been equipped on the primary side of a transducer 7, and the second contact b.sub.1 is connected to the other coil; while the record data D2 lowers to the logical level [0], the transfer switch that has been mounted on the output terminal c.sub.1 is connected to the first contact a.sub.1, and, while the record data D2 raises to the logical level [1], the transfer switch is connected to the second contact b.sub.1 ; in this manner, connection of the transfer switch is sequentially turned, on the basis of the record data D2.
As to the second switching unit 6, the first contact a.sub.2 is connected to the ground, and the second contact b.sub.2 is connected to the transfer switch of the first switching unit 5; while the timing signal ES lowers to the logical level [0], the transfer switch that has been mounted on the output terminal c.sub.2 is connected to the first contact a.sub.2, and, while the timing signal ES raises to the logical level [1], the transfer switch is connected to the second contact b.sub.2 ; in this manner, connection of the transfer switch is sequentially turned, on the basis of the timing signal ES.
At here, a control circuit 8, to which the information of transfer rate for the digital data D1 is given from the exterior, sends the first control signal S1 according to this transfer rate to the first variable current source 9, and besides sends the second control signal S2 based on the quantity of high-frequency-component highlighting according to the transfer rate (as the transfer rate becomes relatively high, the quantity of highlighting becomes large) to the second variable current source 10.
Hereby, the first variable current source 9 generates the first current I.sub.0 that is an origin of the recording current on the basis of the first control signal S1, and the second variable current source 10 generates the second current I.sub.E0 that represents the quantity of high-frequency-component highlighting according to the transfer rate, on the basis of the second control signal S2.
And, in this case, the first voltage source (not shown) for generating the stated positive voltage V.sub.CC is connected to the intermediate tap 7A of the transducer 7, and the second voltage source (not shown) for generating the stated negative voltage V.sub.EE is connected to a terminal 11 to which the output terminals of the first and the second variable current sources 9 and 10 have been connected.
Therefore, while the transfer switch of the first switching unit 5 is connected to the first contact a.sub.1, the first current I.sub.0 that is generated from the first variable current source 9 flows from the intermediate tap 7A of the transducer 7 to the terminal 11 through the first contact a.sub.1 and the output terminal c.sub.1 of the first switching unit 5 and the first variable current source 9 sequentially, and, while the transfer switch of the first switching unit 5 is connected to the second contact b.sub.1, it flows from the intermediate tap 7A of the transducer 7 to the terminal 11 through the second contact b.sub.1, the output terminal c.sub.1 and the first variable current source 9 sequentially.
While, during the transfer switch of the second switching unit 6 is connected to the first contact a.sub.2, the second current I.sub.E0 that is generated from the second variable current source 10 flows from the first contact a.sub.2 that has been connected to the ground to the terminal 11 through the output terminal c and the second variable current source 10 sequentially, and, while the transfer switch of the second switching unit 6 is connected to the second contact b.sub.2, it flows from the intermediate tap 7A of the transducer 7 to the terminal 11 through the first or the second contact a.sub.1 or b.sub.1 of the first switching unit 5, the second contact b.sub.2 and the output terminal c of the second switching unit 6, and the second variable current source 10, sequentially. In this connection, as to the second contact b.sub.2 of the second switching unit 6, the second current I.sub.E0 flows there intermittently in accordance with the switching operation of the second switching unit 6, as shown in FIG. 2D.
As a result of this, through a connection point 12 to which the first switching unit 5, the second switching unit 6 and the first variable current source 9 have been connected, as shown in FIG. 2E, the first current I.sub.0 flows just as it is as a recording original current I.sub.1, while the transfer switch of the second switching unit 6 is connected to the first contact a.sub.2, and, on the other hand, while the transfer switch of the second switching unit 6 is connected to the second contact b.sub.2, the first current I.sub.0 increases by the second current I.sub.E0 (that is, the value of the current becomes I.sub.0 +I.sub.E0), and this flows as the recording original current I.sub.1.
And, the transducer 7 reverses the direction of the recording original current I.sub.1 that flows through the primary side, in response to the switching operation of the first switching unit 5, so as to reverse the polarity of the recording original current I.sub.1 in response to rising to the logical level [1] and falling to the logical level [0] of the record data D2, as shown in FIG. 2F, in accordance with the stated conversion ratio that has been previously set between one or the other coil and the secondary coil, thereby converting it to a recording current I.sub.2 that is formed by highlighting the high-frequency component of the edge portion, and then gives this to a recording head 14 from the secondary side via a rotary transformer 13.
At this time, the relative velocity of the magnetic tape and the recording head 14 in the direction of the recording track is controlled variably, in response to the transfer rate related to the digital data D1, so that the recording head 14 forms magnetization pattern on the magnetic tape, on the basis of the recording current I.sub.2 whose maximum frequency corresponds to the transfer rate and whose high-frequency component of the edge portion is highlighted.
In this manner, this data recorder 1 can previously highlight the high-frequency component of the recording current in accordance with the transfer rate in even the case where the transfer rate varies, and thus it can equalize the high-frequency-component highlighting operations.
By the way, this data recorder 1 is possible to solve the problem that occurs when the above-mentioned linear first and second recording amplifiers are employed, because of employing the recording amplifier 3 that is comprised of a switching amplifier; however, it only equalizes highlighting operations of high-frequency-components of recording currents, and such a problem has been left that it is hard to equalize band limitations of recording current.